The invention relates to false-twist textured yarns made from continuous filaments having modified cross-sections, and is more particularly concerned with polyester yarns that can be draw-false-twist textured for use in fabrics having improved visual aesthetics.
Apparel fabrics knitted or woven from continuous filament synthetic yarns are finding increasing acceptance in the trade. However, texturing is needed to eliminate the undesirable slickness of fabrics made from synthetic filaments. Fabric aesthetics can be further improved by using fibers having a modified (i.e., non-round) cross-section which leads to higher bulk, a crisper and drier hand, better cover and a pleasing subdued luster.
A variety of methods is used to texture filaments depending on the use of the yarn. One which has met with considerable commercial success is false-twist texturing. Unfortunately, fabrics produced from false-twist textured yarns often have an undesirable glitter or sparkle, i.e., reflection of light in intense beams from tiny areas of the fabric. Except for certain novelty applications, this glitter is highly objectionable and detracts from the appearance of the fabric, particularly when the fabric is dyed in dark shades. The propensity to glitter results from yarn changes induced during the false-twist texturing process. In this process, the yarn is twisted, heat-set in the twisted configuration and then untwisted as it exists from the spindle or twist insertion device. The twist-set yarn has a tendency to resume its twisted shape, thus causing the filaments to become crimped and looped, thereby creating bulk and elasticity in the yarn. Under the conditions normally used to false-twist texture yarns, i.e., high twist levels and temperatures above the softening point, the individual filaments in the twisted hot yarn become distorted and tend to form flat surfaces that reflect light in intense beams. Such reflectance is observed as glitter, especially in dark-dyed fabrics prepared from these yarns. When more than about 12% of the filaments in the multifilament textured yarn have cross-sections with a flattened surface or periphery greater than 10 microns in length, then fabrics produced from these textured yarns generally exhibit objectionable glitter. The amount of flattened filament surface or periphery is determinable by examining transverse cross-sectional slices of the yarn under a microscope.
The problem of reducing the size of flat surface deformation sufficiently to overcome objectionable glitter is particularly serious with false-twist textured multifilament polyester textile yarns. When 6--6 nylon filaments are textured, this problem is more easily overcome since such straight chain aliphatic polyamides have better recovery than polyesters from large deformations as occur during false-twist texturing. The problem can also be more easily overcome by using filaments of a sufficiently low denier. However, fine denier filaments provide fabrics which are generally less desirable because they lack crispness and are too soft.
The severity of the problem is compounded when polyester yarns are drawn during the high temperature false-twist texturing operation, since draw-twist texturing generally results in even more severe deformation than false-twist texturing alone. The cross-sections of draw textured filaments which originally possessed round cross-sections are generally asymmetric with one axis several times longer than any other axis in the cross section. This deformation results from high compressional forces caused by simultaneous application of tension and torque to a heat softened filament during drawing. These factors cause greater lateral deformation of the filaments during attenuation. These factors would also be expected to increase deformation or distortion in draw-false-twist textured polyester yarns to such an extent that prior suggestions for obviating glitter in fully drawn yarns that are false-twist textured only would not be expected to be applicable.